The invention relates to a delivery of a sheet-processing machine, in particular, a printing machine, having gripper rows for drawing the sheets, during operation, along a conveying section having endless conveying chains bearing the gripper rows and, during operation, running through the delivery in a revolving direction, having a pair of chain wheels which are rotatable about a common axis of rotation, are in engagement with the conveying chains and form a deflecting region of the conveying section, and having a blast-air source for expelling an air curtain actable upon a side of the sheets being drawn past the sheet-deflecting region, that side being directed towards the axis of rotation of the chain wheels.
Such a delivery has become known heretofore, for example, from U.S. Pat. No. 5,456,178 which discloses an air curtain that is expelled by a blast-tube arrangement coordinated with surroundings of a transfer region wherein a respective gripper row receives a respective sheet from a sheet-guiding cylinder. Once the trailing end of a respective sheet leaves the transfer region, the sheet can then be subjected from this end, i.e., in the sheet travel direction, to blowing action from below. This has extremely adverse effects upon the smooth running or travel of the sheet, however.
In the case of relatively flexurally rigid sheets, in particular, cardboard or pasteboard, the conventional blast-tube arrangement does not provide the desired effect of preventing the sheet from striking randomly against machine parts. Quite contrarily, such a sheet would tend to collide with the conventional blast-tube arrangement.
The published German Prosecuted Patent Application (DE-AS) 20 17 417 discloses a drum provided with a gripper row that receives a sheet from an impression cylinder of a printing unit and transfers it to a following printing unit of a rotary printing machine of unit construction. For reasons not further specified, this drum has a jacket or casing that supports the sheet only along part of the extent thereof in the circumferential direction of the drum. A supporting device that supports the sheet pneumatically is provided in a space located between the sheet-supporting jacket and the gripper row, and covered by the sheets. According to an exemplary embodiment, the supporting device includes a blast tube that extends parallel to the drum axis, is disposed in the vicinity of an envelope positioned on the drum, has blow-out openings which are directed radially outwardly relative to the drum axis and circulates with the drum. This supporting device serves to prevent the formation of a curl in the sheet, the curl formation coming into abutting contact with the blanket cylinder of a respective printing unit as the sheet runs out of the nip, and further to counteract differences in register.
In the case of a delivery such as is mentioned in the introduction hereto, the problem involving the avoidance of differences in register does not arise. Rather, in such a case, there arises the general problem of transferring printed sheets to a sheet conveyor, and combining them into a pile or stack, without smearing. One of the conditions that has to be satisfied in this context is the smooth running or travel of the sheets.
It is accordingly an object of the invention to provide a delivery of the type mentioned in the introduction hereto so as to counteract the blast-air curtain adversely affecting the smooth travel of the sheets passing the sheet-deflecting region.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a delivery of a sheet-processing machine having gripper rows for drawing sheets, during operation, along a conveying section having endless conveying chains bearing the gripper rows and, during operation, running through the delivery in a revolving direction, and having a pair of chain wheels which are rotatable about a common axis of rotation, are in engagement with the conveying chains and form a deflecting region of the conveying section, comprising a blast-air source for expelling an air curtain actable upon a side of the sheets being drawn past the sheet-deflecting region, that side being directed towards the axis of rotation of the chain wheels, the air curtain being movable past the sheet-deflecting region in the same direction as the grippers, while the sheets passing the sheet-deflecting region are being subjected to the action of the air curtain.
In accordance with another feature of the invention, the air curtain is movable past the sheet-deflecting region synchronously with the grippers.
In accordance with a further feature of the invention, the air curtain is directable in a blowing direction with a tendency counter to the running direction of the sheets passing the sheet-deflecting region.
In accordance with an added feature of the invention, the blowing direction of the air curtain is adjustable.
In accordance with an additional feature of the invention, the air curtain is movable past the sheet-deflecting region at an adjustable distance from the conveying section.
In accordance with yet another feature of the invention, the air curtain is movable past the sheet-deflecting region at an adjustable phase angle relative to the grippers.
In accordance with yet a further feature of the invention, the delivery includes a drum body for carrying the blast-air source, and comprises a journal formed with-a cavity and received in a bearing bore of a side wall, the blast-air source being in communication with the cavity, the cavity being in communication with the bearing bore, and the bearing bore being connectable to a compressed-air generator.
In accordance with yet an added feature of the invention, the blast-air source is capable of expelling the air curtain cyclically.
In accordance with another aspect of the invention, there is provided a sheet-processing printing machine, comprising a delivery including at least one of the foregoing features.
In accordance with a concomitant feature of the invention, the sheet-processing machine is a printing machine.
Thus, in order to achieve the object of the invention, the blast-air curtain passes the sheet-deflecting region in the same direction as that of the conveying chains, while the sheets passing the sheet-deflecting region are subjected to the action of the blast-air curtain.
Such a configuration of a delivery avoids, in particular, the situation explained hereinabove wherein the trailing region of the respective sheet is subjected to blowing action from beneath. The reason therefor is that, in particular, in the case of the not absolutely necessary but nevertheless advantageously provided correspondence between the angular speeds of the grippers passing the sheet-deflecting region, on the one hand, and of the blast-air curtain passing the sheet-deflecting region, on the other hand, there is no change in the position of the blast-air curtain relative to the grippers and thus relative to the sheets, which are drawn by the grippers, within the sheet-deflecting region.
An advantageous configuration provides for the blowing direction of the blast-air curtain to be with a tendency counter to the running direction of the sheets passing the sheet-deflecting region, i.e., the blowing direction has a component that is directed counter to the running or travel direction of the conveying chains passing the deflecting region. This makes it possible, in the case wherein the blast-air curtain preferably making contact in a region of a sheet that directly adjoins the grippers drawing the sheet, for the sheet to be subject to the action of blowing or blast air over virtually the entire extent thereof, in the running direction of the sheet, without requiring the blast-air curtain to have, before it makes contact with the sheet, an extent that corresponds largely to the extent of the sheet in the running direction thereof. The blast-air source may thus be of correspondingly small construction, with the result that it may favorably be formed by just one nozzle row arranged transversely to the running direction.
Further preferred configurations provide that the blowing direction of the blast-air curtain be adjustable, that the blast-air curtain passes the sheet-deflecting region at an adjustable distance from the conveying section, and that the blast-air curtain passes the sheet-deflecting region at an adjustable phase angle relative to the grippers.
Utilizing at least one of these conditions, or else a combination of one of these conditions with at least one other, makes it possible for the action which supports sheets passing the sheet-deflecting region to be adapted to a relatively wide range of grammages and degrees of rigidity or stiffness of the sheets, and to different formats thereof, without having to modify the blast-air curtain with respect to the pneumatic parameters thereof. Accordingly, the outlay necessary for producing the blast-air curtain remains relatively low.
A further configuration preferably provides for the blast-air source to expel the blast-air curtain cyclically. Accordingly, the operation of expelling the blast-air curtain can be restricted to a period of time wherein the blast-air curtain passes the sheet-deflecting region in the same direction as the grippers, with the result that it is possible to avoid, in the surroundings of the conveyed sheets, possibly undesired flow states which occur outside the sheet-deflecting region.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a delivery of a sheet-processing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: